KR19990027086A - Plating solution for electro galvanized steel sheet with excellent surface appearance - Google Patents

Abstract

Disclosed is a zinc sulfate bath using an insoluble anode, which prevents stains formed on the surface of the coated steel sheet. The object of the present invention is to provide a galvanized steel sheet having excellent surface appearance that can prevent iron- Thereby providing a plating solution.

In order to achieve the above object, 0.001 to 1.0 g / l of hexamethylenetetramine, which is an iron dissolution inhibitor, is added to a plating solution in order to prevent iron ions from dissolving in a steel sheet during electroplating in a zinc sulfate bath. The present invention relates to a plating solution for use in the production of an electrogalvanized steel sheet having excellent surface appearance, characterized in that dissolution of iron from the steel sheet is inhibited and zinc and iron are simultaneously deposited on the galvanized steel sheet.

According to the present invention, it is possible to prevent blackening of the surface of the steel sheet and generation of partial unevenness by suppressing dissolution of iron ions from the steel sheet during electroplating in the zinc sulfate bath, thereby obtaining an electrogalvanized steel sheet having an excellent surface appearance .

Description

Plating solution for electro galvanized steel sheet with excellent surface appearance

The present invention relates to a plating solution for producing an electrogalvanized steel sheet excellent in surface appearance, and more particularly, to a zinc sulfate bath using an insoluble anode during the production of an electrogalvanized steel sheet, which comprises adding 0.001 to 1.0 g / l of iron dissolution inhibitor The present invention relates to a plating solution for use in the production of an electrogalvanized steel sheet, which is excellent in surface appearance which can prevent stains formed by suppressing the dissolution of iron from a steel sheet and simultaneously allowing zinc and iron to be deposited on the galvanized steel sheet.

When zinc is plated in a sulfuric acid bath employing an insoluble anode, the pH of the solution is controlled to be as low as 1 to dissolve zinc metal having a diameter of about 4 to 5 mm to supply zinc ions because the dissolution rate of metal zinc is increased Zinc ions can be replenished as quickly as the amount of zinc that is precipitated and precipitated. Also, since the pH is lowered due to the low pH, the electrolytic plating solution can be plated with a high limiting current density.

However, the pH of the low solution increases the dissolution rate of the iron ion in the steel sheet to be immersed, resulting in the iron ion being incorporated into the solution.

Therefore, iron ions which are usually dissolved in a plating solution employing an insoluble anodic sulfuric acid bath contain 3 g per ℓ, which causes precipitation on the coated steel sheet to cause surface appearance such as darkening the surface color of the entire steel sheet .

As shown in the following equation, such iron ions are easier to precipitate because they are deeper than the precipitation potential of zinc of -0.76 V, and therefore, they become vacant on the steel sheet simultaneously with zinc.

Zn ²⁺ + 2e ^- ? Zn, -0.76 V (1)

Fe ²⁺ + 2e ^- ? Fe, -0.44V (2)

Iron ions which darken the surface color of the entire steel sheet due to precipitation on the steel sheet as described above will form stains in the flow direction of the solution when the flow rate is uneven and the current density is as high as 60 A / dm ² or more. After the phosphate treatment The outline becomes more pronounced and the surface appearance is damaged.

In order to solve such problems, conventionally, an ion exchange resin method capable of selectively removing only specific ions in a solution was used.

The above-mentioned ion exchange resin process can remove iron ions by using a property that the resin adsorbs iron ions only when a large amount of the ion exchange resin is filled in the large pipe and the plating solution is passed. However, Since the process is required to recover the adsorbed iron ions, the rate is extremely low. In order to treat a plating solution of a large capacity, a large-sized and high-priced facility is required, and the iron ion is controlled to 500 ppm (0.5 g / .

In addition, the ion exchange resin method is disadvantageous in that it is required to be removed after the iron ion is dissolved in the steel sheet.

In order to solve the above problems, the present invention provides a zinc sulfate bath using an insoluble anode, wherein a dissolution inhibitor for preventing the dissolution of iron ions from the steel sheet is added to the solution to prevent surface blackening and staining due to impurities And an object of the present invention is to provide a plating solution for manufacturing an electrogalvanized steel sheet excellent in surface appearance.

FIG. 1 is a graph showing the influence of the addition amount of hexamethylenetetramine in the zinc sulfate plating solution having a pH of 1.0 and a temperature of 24 ° C on the dissolution of iron oxide.

In order to accomplish the above object, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an electrolytic galvanized steel sheet having excellent surface appearance in an insoluble zinc sulfate bath, To thereby prevent the dissolution of iron ions dissolved from the steel sheet, thereby providing a plating solution for the production of an electrogalvanized steel sheet excellent in surface appearance.

Hereinafter, the present invention will be described in more detail.

In general, galvanized steel sheet is used mainly for the purpose of improving the corrosion resistance of steel sheet because it has excellent sacrificial force against the base metal. It also has various advantages such as low cost, high speed gold plating and no harm to human body. Because of its silver-white beauty, it has been widely used as a material for consumer electronics.

The galvanized steel sheet can be classified into a hot dip galvanizing method and an electroplating method according to a method of plating zinc on a steel sheet. The hot dip galvanizing method is a simple method of plating a steel sheet through a hot molten pot while the electroplating method is used for productivity, Various plating baths and solution conditions have been applied.

Electroplating baths can be broadly divided into horizontal, vertical, and radial types, and the solution composition and plating conditions vary depending on these baths.

A system based on sulfuric acid as a plating solution employs a double insoluble anode, and a system for supplying zinc ions by dissolving metal zinc as a plating solution in order to reduce the incorporation of impurities from zinc and improve workability.

In order to dissolve the metal zinc in the plating solution as described above, the pH of the solution is maintained at about 1.0. The pH of the solution increases the dissolution rate of the base steel sheet, which results in the iron ion being incorporated into the solution as an impurity As such impurities, iron ions cause simultaneous precipitation reaction with zinc to blacken the surface of the plating, and when the flow velocity is uneven and the current density is high, the amount of iron precipitation increases, and the iron content locally on the surface of the steel sheet is uneven, do.

In particular, when the phosphate treatment is carried out, such a stain appears more clearly, so that the surface quality is largely lowered and the product value as a product is lost.

For this reason, as shown in FIG. 1, 0.001 to 1.0 g / L of a dissolution inhibitor such as hexamethylenetetramine, which selectively inhibits the dissolution of iron, is added to produce an electrodeposited steel sheet having excellent surface appearance.

The reason for limiting the numerical value in the present invention is that addition of hexamethylenetetramine, which is an iron ion dissolution inhibitor, at a concentration of 0.001 g / L or less lowers the effect of inhibiting the dissolution of the steel sheet. When the addition amount of 1.0 g / L or more is exceeded, This is because high current density plating is difficult because the time limit current density is lowered.

When the steel sheet is immersed in a corrosive solution such as an acid, the surface of the steel sheet forms a local cell that forms an anode and a cathode because of physical irregularity of the surface or chemical properties of the surface of the steel sheet .

Here, the steel sheet acts as an oxidation reaction (anodic reaction) and dissolves as shown in the following equation. On the other hand, a hydrogen gas generation reaction occurs in a reduction reaction (cathode reaction).

Oxidation reaction (anodic reaction) Fe → Fe ²⁺ + 2e ^- (3)

Reduction reaction (cathode ^{reaction) 2H + + 2e - → 2H} → H 2 ↑ ········· (4)

When hexamethylenetetramine [(CH ₂ ) ₆ N ₄ ], which is a dissolution inhibitor of the steel sheet, is added during the above reaction, the inhibitor is adsorbed physically or chemically on the surface of the steel sheet to inhibit the acid solution from dissolving the steel sheet.

These dissolution inhibitors consist of polar groups which have a direct adsorption action on the surface of the steel sheet and organic atomic groups which do not adsorb directly to the surface of the steel sheet but which are bonded to polar groups and protect the surface of the steel sheet to prevent dissolution by acid.

Therefore, among the elements constituting hexamethylenetetramine, the polar group is N and the organic atomic group is CH ₂ .

Hereinafter, the present invention will be described in more detail with reference to examples.

Example

First, to measure the rate at which the substrate iron dissolves in the plating solution, the specimen is uniformly cut at 4 × 5 cm, then degreased and measured for weight. Then, hexamethylenetetramine, a dissolution inhibitor, is added to the plating solution composition shown below at 0 to 2.0 g / ℓ, and the dissolution amount of the substrate was measured after a certain time at room temperature.

In order to investigate the critical current density while plating the specimen at 100 A / dm ² using a large plating bath under the following plating conditions while varying the amount of hexamethylenetetramine added to the solution composition below, the width of the burning occurred at the edge of the specimen Were measured.

The size of the negative electrode specimen used for plating was 100 × 200 mm, the amount of plating was 20 g / m ² , and the gap between the plating baths was 15 mm.

[Zinc plating conditions]

(1) Plating solution composition

Zinc: 63 g / l

Sodium sulfate: 100 g / l

Hexamethylenetetramine: 0 to 2.0 g / l

(2) Plating conditions

Temperature: 60 ° C

pH: 1.0

Current density: 100 A / dm ²

Plating adhesion amount: 20 g / m ²

Flow rate: 1.5 m / sec

Table 1.

division The amount of hexamethylenetetramine added to the plating solution (g / l) The amount of dissolution (g / m < ² > hr) Burning occurrence width (mm) after plating turn Conventional example 0 6.81 0.15 One Comparative Example 0.0005 3.52 0.13 2 2.0 0.4 2.3 3 Honorary honor 0.001 0.96 0.15 4 0.05 0.71 0.24 5 0.1 0.65 0.26 6 0.5 0.45 0.44 7 1.0 0.41 0.51 8

In Table 1, the dissolution rate of the steel sheet was 6.8 g (m ² ) per one surface hour of the steel sheet in the case of not adding hexamethylenetetramine, whereas in the present example, hexamethylenetetramine was dissolved in an amount of 0.001 g / It can be seen that the dissolution rate of iron is reduced by about 7 times.

However, as shown in the comparative example, when the dissolution inhibitor is used in excess, the dissolution rate of the iron oxide can be suppressed, but the quality of the product is deteriorated due to burning of 2 mm or more on the edge of the steel sheet during plating.

According to the present invention, it is possible to prevent the blackening of the surface of the steel sheet and the generation of partial unevenness by suppressing the dissolution of iron ions from the steel sheet during electroplating in the zinc sulfate bath, thereby obtaining an electrogalvanized steel sheet having an excellent surface appearance Effect is obtained.

Claims (1)

In an electrogalvanizing solution composed of sulfuric acid and zinc, Characterized in that hexamethylenetetramine [(CH ₂ ) ₆ N ₄ ] is added to the solution in an amount of 0.001 to 1.0 g / l.